Uses for Vegetable Oils

by Marvin O. Bagby. Research Leader Oil Chemical Research, National Center for Agricultural Utilization Research, ARS, USDA, Peoria, IL.

American agriculture produces over 16 billion pounds of vegetable oils each year. These domestic oils are extracted from the seeds of soybean, corn, cotton, sunflower, flax, and rapeseed plants.

Although more than 12 billion pounds of these oils are used for food products such as shortenings, salad and cooking oils, and margarines, large quantities serve feed and industrial needs. The latter applications include chemicals such as plasticizers, which add pliability to plastics and other substances; stabilizers, which help other substances resist chemical change; emulsifiers, which enable the mixing of normally unmixable liquids; surfactants, which reduce the surface tension of liquids and are commonly used in detergents; and esters, nylons, and resins, which are basic ingredients in many industrial products. Besides detergents and plastics, products that contain chemicals derived from vegetable oils include lubricants, coatings, corrosion inhibitors, adhesives, cleaners, cosmetics, water repellants, and fuels.

The three domestic oils most widely used industrially are soybean, linseed from flax, and rapeseed. The relatively low cost of soybean oil and its dependable supply make it one of the more important oils; it provides nearly 80 percent of the seed oil produced annually in the United States. Other vegetable oils widely used industrially include palm, palm kernel, coconut, castor, and tung, but these are not of domestic origin.

Nonfood uses of vegetable oils have grown little during the past 30 years. Although some markets have expanded and new ones have been added, other markets have been lost to competitive petroleum products. Public and private researchers are seeking to develop new industrial products or commercial processes. Through these efforts, vegetable oils should maintain or even add to their market share while petroleum, which is nonrenewable, becomes more expensive.

Research and development approaches frequently take advantage of the natural physical or chemical properties of the oils or their major constituents fatty acids and glycerol but it is often advantageous to modify these properties for specific applications.

Vegetable oils are too viscous and too reactive with atmospheric oxygen to establish significant markets for use in cosmetics, lubricants, and certain chemical additives. Fortunately, properties such as viscosity, pour point, freezing point, and reactivity can be decreased by chemically introducing branching groups or side chains on the straight-chained fatty acids. For example, derivatives of isostearic acid, a byproduct of commercial dimer acid manufacture, can be used in many products textile lubricants, softeners, and antistatic agents; coupling agents; emulsifiers; greases; and synthetic lubricants for which the unmodified oil would be too reactive.

Conversely, to make certain products, vegetable oils must be made more reactive. By changing a domestic oil's physical properties, it can be made to resemble and replace imported tung oil in coatings, resins, ink vehicles, and plastics.

Markets for these highly reactive oils are expected to grow with the increasing sophistication of consumers worldwide and with changing and more stringent product performance requirements.

Scientists at USDA's Agricultural Research Service (ARS) pioneered much of the research that established industrial markets for vegetable oils. Most ARS research on industrial uses for fats and oils takes place at the National Center for Agricultural Utilization Research (NCAUR), Peoria, IL; the Eastern Regional Research Center (ERRC), Philadelphia, PA; and the Southern Regional Research Center (SRRC), New Orleans, LA.

Epoxidized Oils and Films. During World War II, ERRC scientists developed methods for converting vegetable oils to epoxidized oils, for use as plasticizers and stabilizers. Epoxidized oils are highly compatible with commercial resins, and they are nonvolatile. They are also effective stabilizers, thus eliminating the undesirable toxic stabilizers that were previously necessary. Out of the 300 million pounds of soybean oil used annually for industrial products, nearly 122 million pounds are converted to epoxidized oil. Other oils, mainly linseed, produce an additional 15 million pounds.

Linseed oil, containing about 60 percent linolenic acid, reacts rapidly with oxygen in air to form insoluble, flexible, adherent films which are used in paints and coatings. Although its use in paints has plateaued as a result of competition from other technologies, many paint formulations still contain linseed oil because of its superior adhesion characteristics. Also, NCAUR technology has demonstrated that formulations of linseed oil may be used to cure and protect concrete.

Rapeseed oil is principally useful as a source of erucic acid, a long-chain fatty acid consisting of 22 carbon atoms. Derivatives of erucic acid are used in the plastics industry as antiblocking or antistatic agents to make plastics less sticky and self-adhering and therefore easier to work with.

Research and development begun by NCAUR in the early 1940's led to the commercial production and use of polyamide resins. Polyamides are prepared from dimer acids that have been derived from soybean and other vegetable oils and are used as hot-melt adhesives for shoe soles, book bindings, can-seam solders, and packaging. Production of dimer acids in the United States is about 40 million pounds per year; perhaps more than half of this is used for polyamides. Because polyamides have flexibility, adhesion, and resistance to chemicals and moisture, they are used in flexigraphic inks and moisture-proof coatings. Polyamides are also used to make drip- and sag-resistant paints that do not need stirring and that will not be absorbed into porous surfaces such as open-grained wood and cinderblocks. Two-part adhesives (epoxy resins and polyamide curing agents) are widely used today and are made from the polyamides developed from this ARS research.

Nylon 9

Nylon 9, a product of NCAUR research, is a plastic made from oleic acid, a fatty acid found in most vegetable oils, including soybean, cottonseed, and sunflower. Because nylon 9 has a low moisture absorption rate, it does not warp and it is a better electrical insulator than nylon 6, a commonly used, and otherwise comparable, plastic derived from petroleum. Nylon 9 is slightly stronger than nylon 11 and nylon 12, two plastics which have properties similar to nylon 9. Because nylon 9 can withstand high temperatures, it has potential as an excellent material for making molded objects that will be subjected to large variations in air temperature, for example grills on automobiles. Its low rate of moisture absorption makes it ideal for products that require electrical and water resistance, for example insulators and water pumps.

Chemist Sevim Erhan compares soybean oil with the traditional petroleum-based product used in the manufacture of printing ink. Soy oil is a much lighter colored vehicle for producing ink.

Keith Weller/USDA 91BW2345

Soybean Oil Inks

Soy inks, alternatives to conventional petrochemical-based inks, were developed by the American Newspaper Publishers Association (ANPA) and were first used in 1987 by the Cedar Rapids Gazette (IA). The ink from soybeans consists of about 50-60 percent degummed soybean oil, 20-25 percent petroleum resin, and 15-25 percent pigments. This ink has gained rapid acceptance by the newspaper industry. The colored inks are especially popular. Because the black inks formulated by the ANPA were not cost-competitive with typical offset news inks they are not widely used.

The technology for making soy inks consists of a direct substitution of soybean oil for the mineral oil portion of the vehicle (the entraining and dispersing agent for the pigments and other solid substances). Therefore, other oils that have a fatty acid composition similar to that of soybean oil should be directly interchangeable. In fact, some formulators have prepared inks from mixtures of soybean and corn oils. Economic considerations and marketing strategies govern the selection of the oils used in the formulation.

At the request of ANPA and the American Soybean Association, NCAUR recently developed a technology in which the vehicle is totally derived from vegetable oils. Although soybean oil was emphasized because of its dependable supply and low cost, this new technology was demonstrated with several commodity oils. Besides replacing petroleum, this technology permits formulation of inks over a broader range of viscosity as well as inks that are more cost-competitive with conventional offset news inks. Further, inks formulated with this technology have rub-off characteristics equal to those formulated and marketed as low rub-off inks.